Receiver



' Sept. 20, 1927.

TRANSMISSION UNITS W. C. JONES RECEIVER Filed OOt/ 50, 1924 /2 f /5 /7 /9 I I AMPERE TU RNS m Patented Sept. 20, 1927.

UNITED STATES 1,642,777 PATENT OFFICE.

WARREN C. J' ONES, OF FLUSHING, NEW YORK, .ASSIGNOR TO WESTERN ELECTRIC COM- PANY, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK.

RECEIVER.

Application filed October 30, 1924. Serial No. 746,791.

This invention relates to telephone receivers, and its object is a telephone receiver of improved efficiency and moreover one that is stable in its operating characteristics under severe service conditions.

The invention is particularly applicable to subscriber station receivers of the electro magnetic type, although it is not limited to this type. The requirements for a receiver of this type are of such a nature that it is not only necessary that the receiver be an eflicient transducer for converting the electrical energy of the speech currents into sound energy, but it should preferably reach its maximum efficiency at a low magnetizing current such as would be present on long subscriber loops where'the attenuation is a maximum. Furthermore, the construction of the receiver should be such that its efficiency of operation is not materially altered when the instrument is subjected to wide temperature variations such as might be experienced in extreme cases.

In a receiver of this type, there are two forces which play an important part in determining its characteristics; namely, a variable force resulting from the combined action of the polarizing and variable fluxes and a steady force due to the polarizing flux alone. The former constitutes the useful driving force, and the latter owing to the control which it exerts over the reluctance of theair-ga influences not only the efliciencyat sma l magnetizing currentsbut is instrumental in determining the magnetizing current at which maximum efiiciency occurs. The magnitude of the steady force resulting from the polarizing flux at high magnetizing currents also has an important bearing on the stability of the receiver, since it 'is influential in determining the minimum separation which may be employed between the diaphragm and the pole pieces. There is also a third force which acts u on the diaphragm; namely, a variable orce which is proportional to the square of the variable flux and which is an octave higher in frequency than the voice current. ceiver the magnitude of the polarizing flux is suflicient to render the influence of this variable force negligible and to remove any distorting effect due to the double frequency.

.On long subscriber loops where the mag However, in a Well designed re-- netizing current is small and the flux density in the diaphra m and the pole pieces is the magnitude of the polarizlng flux and since a given polarizing flux is required to bring the magnetic circuit up to its maximum efliciency, it follows that the length of air-gap thus fixes the minimum magnetizing force or ampere turns necessary to-bring the magnetic circuit to maximum 'efliciency. Therefore, so far as the iron portion of the magnetic circuit is concerned the effective permeability of the material becomes the most important factor in determining the useful driving force. Since for a given receiver the magnetizing current is determined by the resistance external to the receiver, the magnetizing force necessary for establishing the polarizing flux is dependentupon the number of turns in the winding, a fact which obviously reacts upon the electrical impedance of the receiver. This impedance, if maximum operating efliciency is to be obtained, is fixed by the electrical impedance of the apparatus at the subscriber station and by the acoustic impedance of the ear, since under these conditions the impedance looking into the receiver must be the same as the impedance looking towards the line. In the case of the present subscriber sets this impedance does not permit winding the receiver with a sufficient number of turns to provide the magnetizing force necessary to bring the circuit up to maximum efficiency. It therefore follows that in order to meet the impedance requirement and still have the receiver reach its maximum efli ciency under severe conditions such as exist on long loops, it is necessary to sacrlfioe magnetlc efiiciency and arrange the circuit in such a manner that one member, either the pole structure or the diaphragm, approaches saturation at a magnetizing current equal to that obtainable on long loops. This condition is best met by employing a diaphragm of low mass and of a material and thickness such that it approaches saturation at low current values since as a result of the low mass the unbalance in the acoustic impedance between the receiver and the ear load is to a certain extent corrected.

In accordance With a feature of the invention, the diaphragm and pole pieces are so dimensioned and spaced with respect to each other that the receiver reaches its maximum efficiency at much lower magnetizing forces than has been possible heretofore.

In accordance with another feature of the invention, by the addition of a plate which serves as a magnetic shunt and becomes effective only at the higher magnetizing forces, the efficiency of the instrument for short loops is increased.

Still another feature consists in constructing the magnetic portion of the receiver so that changes in temperature will not cause marked variation in the operating air-gap which will be reflected in the efliciency of the receiver.

These and other features of the invention may be more clearly understood by reference to the accompanying drawing, in which Fig. 1 is an explodedview in perspective of a preferred form ofelectromagnetic re ceiver embodying the features of the invention;

Fig. 2 is a view partly in section of the assembled receiver shown in Fig. 1;

ployed in this construction; and

In Fig. 4 are curves showing the improved eificiency obtained by following this construction.

Referring more particularly to Figs. 1 and 2, the o erating coi 5 assembled on ,the center leg 6 0 an E-shaped pole piece, is mounted within a cup-shaped member 7 having a flanged portion 8. The pole piece consists of two U-shaped members 9, 9 positioned as shown to provide the common central leg 6 and are welded or otherwise intimately secured to the plate 10, which in turn is secured to the bottom of cup-shaped member 7 40 by means of screws 11. The flanged portion 8 is provided with a peripheral rmg 12 adapted to serve'as a seat for the diaphragm 13. A late member 14 provided with a series o perforations 15, 15 is adapted to be mounted adjacent the diaphragm and serve as a magnetic shunt therefor in the manner to be explained hereinafter. The flanged portion 8, diaphragm 13 and plate 14 are assembled as a unit and are clamped together by means of an inner clamping ring 16 threading into an outer clamping ring 17. This assembled unit is adapted to be mounted in a standard form of receiver cup 18 which may be either of metal or of an insulating material such as hard rubber and bn which is threaded a receiver cap 19 which also serves as an ear piece. 7

I The ole pieces 9, 9, diaphragm 13 and prefera ly the plate 14 are composed of a magnetic material having an effective permeability at low magnetizing forces very much higher than that of iron, a lower hysteresis factor, and a resistivity of the order of 45 microhms per centimeter cube. To obtain 65 this material, iron and nickel are fused to- Fig. 3 is a view of the magnetic shunt em- 1 form to be worked over for this purpose.

While 55% iron and 45% nickel have been mentioned as being the proportion of the ingredients of nickel and iron preferably to be employed in making up this material, it should be understood that this proportion may deviate from these figures and, under certain conditions, it may even be desirable to add a third element. Thus, for example, if the composition consists of 21 iron and 7 8 nickel, a'material having an even higher permeability than that of the 55% iron, 45% nickel composition is obtained, but 8. this latter composition has a considerably lower resistivity. By the addition of approximately 1% chromium to the 21 iron, 7 8 5% nickel the resistivity is increased all to approximately that obtained with the 55% iron, 45% nickel composition.

To develop the utmost permeability of the magnetic material, the finished parts are subjected to a heat treatment which, for particular cases, varies somewhat as regards the tempertures employed and the duration of the heating and cooling periods. The optimum values of these variables may readily be determined for a specific case by experi ment. In the case of the preferred composition, consisting of 55% iron and 45% nickel,

a suitable heat treatment has been found to be to heat the material to a temperature of 1100 C. and then to'cool at the rate of approximately 4 C. per minute. This rate of cooling is not critical but can be varied over wide limits. The magnetic material obtained in this manner has an extremely high effective permeability at low magnetizing forces and saturates at a point considerably 11o below that of magnetic iron. The effective permeability of this material to small alternating currents with various values of direct current superimposed is shown graphically in a copending application of George W. 11 Elmen Serial No. 747,718 filed Nov. 4,1924,

After the heat treatment, the material, to maintain a high. constant value of permeability must be guarded against any considerable strains, and therefore this treatment is preferably applied to the material in its finished form.

In Fig. 4 are curves showing-the improvement in operating efliciency resulting from embodying the various features of the invention in the magnetic'circuit of a receiver. Curve A shows the improvement in transmission units or mile-s gained in transmission with an electromagnetic receiver employing the improved alloy for pole pieces but with a standard ferro type diaphragm, as compared with a standard type of subscribers station receiver. Curve B shows the additional improvement resulting from replacing the ferro type diaphragm with a diaphragm of the proper'thickness composed of the improved alloy. Curve C shows the gain in efficiency at high magnetizing currents when employing a mag netic shunt for the diaphragm.

Referring to curve A, it will be noted that with the use of the nickel-iron alloy containing nickel and properly heat treated in the pole pieces of the receiver, there results a maximum gain in efiiciency equivalent to four transmission units while a gain of two transmission units or better is obtained over the entire working range. The winding of this receiver consisted of 1,200 turns, and since the maximum gain Wasattained at a magnetizing current of milliamperes,-the maximum efliciency was obtained with an energizing force of ampere turns. By replacing the ferro type diaphragm with a diaphragm of the proper thickness composed of the nickel-iron alloy containing 45% nickel, there results, as

shown on curve B, a maximum gain in efliciency equivalent to nine transmission units, but what is even more important this maximum gain is obtained with a smaller magnetizing current, approximately 35 milliamps-res, which corresponds to an energizing force of 42 ampere turns. It will be seen that curve B drops ofl rapidly slightly beyond its maximum point and approaches curve A. This rapid drop in efliciency is due to the early saturation of the diaphragm and it was to overcome this "rapid decrease in efliciency that the plate 14 of Fig. 1 was positioned adjacent to the diaphragm to serve as a magnetic shunt therefor by carrying a portion of the flux after the diaphragm has become saturated. The improvement gained b the use of this plate is shown strikingly 1n curve C, from which it will be seen that, by its use, there results a slight gain in maximum efficiency and this gain decreases slowly so that wit a magnetizing current of 90 milliamperes, which corresponds to a short subscribers loop, the efiiciency is still approximatel six transmission units better than that o the standard type of substation receiver. The improvement that can be effected by a magnetic shunt is determined largely b the minimum separation necessary to insure stable operation, sincethe shunt plate in relieving ,the saturated condition of the diaphragm increases the deflection ofthe diaphragm for a given magnetizing current, and causes the diaphr m to be drawn into contact with the pole pieces when operating at the larger magnetizing forces. Under normal service conditions this separation should be approximately fifteen thousandths of an inch and in no caseless than ten thousandths of an inch. I

In order to obtain the maximum efiiciency of the receiver, it is necessary to reduce the separation between the diaphragm and the pole pieces to the minimum value consistent with stable operation, and in this connection it is necessary to eliminate, so far as possible, all variation due to changes in temperature. An analysis of the causes underlying the fluctuation in efficiency which accompanies a change in temperature .has shown that these changes are due to a change in actual separation between the diaphragm and pole pieces, arising fro-m unequal radial expansion of the diaphragm and its clamping surfaces, and unequal linear expansion of the magnetic unit and its supporting structure, the former being much the more important factor. To minimize these effects, the material composing the clamping surfaces should have the same linear temperature coefficient of expansion as the diaphragm, and a similar relation should exist between the unit and its supporting structure. In accordance with the present invention, the changes in efliciei'icy due to changes in temperature have been reduced to a minimum by providing a material having the same temperature coefficient for the diaphragm, pole pieces, and clamping members. An electromagnetic receiver embodying the features of this invention was tested for transmission efiici-cncy, then subjected to a temperature of 20 below zero F., after which it was raised to a temperature of 160 F. and then allowed to cool to room temperature, whereupon it was tested and found to have shown no appreciable change in efliciency. Furthermore, in this construction arrangements are made for clamping the various portions of the magnetic structure together, thus obtaining the advantages of unit construction.

What isclaimed is:

1. In a telephone receiver, an energizing winding, a magnetic circuit therefor includlih) ing a vlbrating diaphragm approaching saturation at low ma netizing forces, and means for relieving t e saturated condition of the diaphragm.

2. In a telephone receiver, an energizing winding,- a magnetic circuit therefor including a vibrating diaphragm approaching saturation at low magnetizing forces, and a magnetic shunt for said diaphragm.

3. In a telephone receiver, an energizing winding, a magnetic circuit therefor including'a vibrating diaphragm approaching saturation at low magnetizing forces, and a magnetic member mounted adjacent the diaphragm thereof. 7 a

4. In a telephone receiver, an energizing to relieve the saturated condition winding, a magnetic circuit therefor including a vibrating diaphragm approaching saturation at low magnetizing forces, and a magnetic shunt for said diaphragm operable only upon large magnetizing currents traversing said winding to relieve the saturated condition of the diaphragm.

5. In a telephone receiver, an energizing winding, a magnetic circuit'therefor including pole pieces and a vibrating diaphragm saturated at low magnetizing forces and a magnetic plate mounted adjacent to but separated from the diaphragm at portions in alignment with the pole pieces by an air gap of not less than .010 of an inch.

6. Ina telephone receiver, an energizing winding, a magnetic circuit therefor including a vibrating diaphragm saturated at low magnetizing forces and a magnetic shunt composed of a' material having a higher permeability than iron at low magnetizing forces and'a lower saturation point.

7. In a telephone receiver, an energizing Winding, a magnetic circuit therefor including a vibrating diaphragm saturated at low magnetizing forces, and a magnetic shunt composed of an alloy containing substantially nickel and 55% iron.

8. In a telephone receiver, an energizing winding, pole pieces therefor, a thin vibrating diaphragm capable of being saturated at low magnetizing forces, and means for relieving the-saturated condition of the diaphragm when operating at high magnet1z-. ing forces.

ergizing winding, a magnetic circuit thereof less than ampere turns.

12. In an electromagnetic receiver, an enfor composed of an alloy containing approximately 45% nickel and iron, said magnetic circuit being so proportioned that the receiver reaches its maximum efiiciency at an energizing force of less than 5.0 ampere turns.

13. In an electromagnetic receiver, an energizing winding. a magnetic circuit therefor including a vibrating diaphragm, said diaphragm being composed of an alloy containing approximately 45% nickel and 55% iron, and having a thickness of approximately .006", said diaphragm being separated. from the pole pieces by an air gap of approximately .008.

14. In a telephone receiver, an energizing winding, a magnetic circuit therefor including a vibrating diaphragm, a magnetic shunt for said diaphragm, and means for locking said parts in position to provide a unitary structure.

15. In a telephone receiver, an energizing winding, a magnetic circuit therefor including a vibrating diaphragm, a magnetic shunt for said diaphragm, and a pair .of clamping rings cooperating to lock said parts in position to provide a unitary structure.

In witness whereof, I hereunto subscribe my name this 28th day of October A. D., 1924.

WARREN C. JONES. 

